Long-term Expectations for the Non-Removable Battery

So, as the positive reviews of the Maxx's "ridiculous" battery life roll in, I believe a legitimate concern should be addressed regarding its projected capacity as the battery degrades over time. Given that many of us will have this phone for 1-2 years, to what extent should we expect a significant decrease in our ability to use this phone freely as we near the end of the contract?

With proper care, Li-ion batteries (and Li-ion polymer) have a lifespan of around 2-3 years or ~350 (full) cycles. I believe that "life" is considered expired when the battery reaches ~70% of its original capacity. Thus, with a 3,300 mAh battery, a basic number crunch would imply that at the end of a standard 2-year contrast, the Maxx's capacity would be only ~2,310 mAh. That is a serious drop, especially when phones with removable batteries have the option of switching packs to always maintain a large capacity. (g-nex extended + stock = ~3900 mAh, which can be replaced to prevent deterioration)

Can any battery experts/mathematicians weigh in on what the Maxx's now-excellent battery life might look like 2 years down the road? Or does anyone have useful tips for prolonging the life of the non-removable battery?